An aerosol exposure sensor and sampler is utilized to sample the aerosol in the immediate vicinity of the aerosol exposure monitor to enable the breathing zone aerosol particles to be analyzed by any number of different techniques. The aerosol exposure monitor may be designed for indoor, outdoor, or personal use. A personal exposure monitor is typically designed to be worn by a person to sample the aerosol in that person's breathing zone.
Aerosol sampling may be done over a specified period of time (integration period). The aerosol exposure monitor may be configured to aerodynamically size and then collect particles during the integration period, after which the collected particles are analyzed. As an example, the aerosol exposure monitor may include a sample inlet that leads to a housing that contains a substrate. The substrate, for example a filter, is configured to enable particles of a desired size range to accumulate thereon. At the conclusion of the integration period, the substrate may be removed and subjected to one or more types of destructive or non-destructive analyses. This type of aerosol exposure monitor is useful for enabling the acquisition of chronic or long-term exposure data, but is limited by the fact that it is not able to perform any type of measuring, sensing or detecting function in real time during the integration period. That is, this type of aerosol exposure monitor merely collects a total population of one or more types of particles over the integration period, after which one or more separate analyses must be done to acquire data that may be integrated or averaged over the integration period. This type of aerosol exposure monitor may be passive or active. A passive monitor relies on natural aerosol flow applying convection rather than diffusion to size and collect the aerosol. A passive monitor can be a low-burden (as to size, weight, and quietness) device, with little or no energy requirements, but does not collect them aerodynamically and collects so few particles that analytical techniques such as gravimetric mass analysis are either extremely limited or impossible.
On the other hand, an active monitor includes some type of fluid-moving device (typically a pump) to positively establish a flow of aerosol into the sizer of the active monitor. An active monitor may enable robust particle collections, and also facilitates the inclusion of an aerosol impactor in the active monitor and thus enables aerodynamic sizing of the particles being sampled. An active monitor, however, requires more power than a passive monitor due to the need for operating the pump. In the case of a personal exposure monitor, batteries are utilized to supply power and thus the additional power required for the pump limits the duration of the aerosol sampling period. Moreover, an active monitor is typically burdensome due to the inclusion of the pump, associated plumbing, possibly an aerosol impactor, and in personal applications a battery pack. In addition to being larger and heavier than a passive monitor, the active monitor has conventionally been noisy due to the operation of the pump. The higher burden typically imposed by an active monitor poses a significant wearing compliance problem in the case of personal exposure monitors. In particular, the person to be monitored may be required to wear the active monitor during prescribed intervals of time and during certain activities (which may include exercise or other activities involving a high level of motion and personal exertion) over the course of the sampling period. The acquisition of valid data from the personal exposure monitor thus requires “wearing compliance” by the person. The higher the burden imposed by the active monitor, the less likely wearing compliance will occur. As an example, recent testing of personal monitors has shown that the majority of elementary age children are not comfortable with sensor systems that weigh more than 300 grams and add more than 5 decibels to the environment.
Another type of aerosol exposure monitor may be configured to acquire data from the aerosol being sample in real time during a prescribed sampling period. One example is a nephelometer, which typically measures particles in a fluid stream by illuminating the particles and detecting the resulting light that is scattered from the particles. Unlike a turbidometer, which measures the effects of high concentrations of particles, a nephelometer is designed to measure both low and high concentrations of particles. A nephelometer measures particle concentration in real time and thus would be useful in the context of a personal exposure monitor for acquiring peak exposure data. To be convenient to carry and use, the nephelometer should be as small and compact as possible. The nephelometer should also be highly sensitive to the entire range of concentrations of particles the wearer might encounter.
In view of the foregoing, there is an ongoing need for aerosol exposure monitors that present extremely low burden and thus are useful as personal devices that are easily wearable by users. It would also be useful to provide an aerosol exposure monitor capable of simultaneously acquiring both chronic and acute exposure data. There is also a need for active aerosol exposure monitors capable of operating without excessive noise.